Hello all,

I have a 2003 Jaguar S Type R. It recently developed fuel pressure problems to the point that it was undriveable. I took it to a shop and they replaced one of the fuel pumps and that seemed to do the trick. It now drives relatively normal as long as I don't drive it like a racecar. That said, there is still a check engine light on and the codes are for cylinder misfires. If it is driven hard to the point of using the super charger it develops a fuel pressure problem again. The mechanic told me it needs a new throttle body. I asked if the current one was broken or in need of cleaning and they told me they tried cleaning it and reinstalling it, but it did not work and that I need to get a new throttle body. That leads to my question...

If the old throttle body was cleaned and appeared functional then what is the difference between that and a new throttle body? I assume that when cleaning it, if something was physically wrong with it, they wouldn't bother trying it. What is the difference between a cleaned old one and a new one? If they took the old throttle body off and cleaned it and deemed it functional and it still didn't solve the problem then is the throttle body the problem?

I'm just trying to educate myself about throttle bodies before I tell the shop to order the part.
Thoughts?

 

Can you please define "fuel pressure problem"? What symptoms do you experience? Does it set a code for fuel pressure out of limits? Does a scanner show low fuel pressure? Does the engine stutter or lose power?

The STR has two fuel pumps to handle the increased fuel flow during high power demand. If a scanner is showing low fuel pressure when you stomp on it, perhaps only one pump is working.

 

It is likely NOT the TB (but could be). Leave it until you know far more.

Record the fuel trims. Hot engine, parked. At idle & at highish revs, about 2500 - you may just have an air leak.

But if you have a fuel pressure problem then don't go messing with the TB! It's a precision part with special coating.